The present invention relates to cells for the conversion of radiant energy to electrical energy, such as solar cells. The invention is particularly concerned with the type of cells known as back-wall cells.
In solar cells heretofore proposed, it has been known to provide on a first semiconductor material of one conductivity type, a thin layer of the opposite conductivity type semiconductor material forming between the interface a semiconductor p-n junction and arranged to receive the radiation. On the opposite face of the first semiconductor material may be applied a further semiconductor material of the same conductity type but of higher conductivity, that is, more highly doped. In operation, the radiant energy is received on the layer of opposite conductivity type, is absorbed and results in the formation of electron-hole pairs at or about the junction interface. The electrons are collected on the n material side of the junction, whereas the holes or positive carriers are collected on the p side of the junction. Accordingly, if suitable connection, such as a conductive grid, is provided on the radiation receiving layer, a suitable conductive connection to the further material of higher conductivity, and a load connected between them, a useful electrical current may be caused to pass through the load.
Such devices are described, for example in U.S. Pat. No. 3,359,137 to Stephen Kaye et al., issued Dec. 19, 1967 for "Solar Cell Configuration," U.S. Pat. No. 3,460,240 to Tarneja et al. issued Aug. 12, 1969 for "Manufacture of Semiconductor Solar Cells," and U.S. Pat. No. 3,462,311 to Ross issued Aug. 19, 1969 for "Semiconductor Device Having Improved Resistance to Radiation Damage." Other illustrative patents are U.S. Pat. No. 3,852,591 to Lee et al issued Dec. 3, 1974 for "Graded Band-Gap Semiconductor Photo Detector for Equalization of Optical Fiber Material Delay Distortion"; U.S. Pat. No. 3,838,439 to Biard, issued Sep. 24, 1974 for "Phototransistor Having a Buried Base"; and U.S. Pat. No. 3,675,026 to Woodall, issued July 4, 1972 for "Converter of Electromagnetic Radiation to Electrical Power."